1. Field of the Invention
The present invention relates generally to chains used in wastewater treatment plants that produce sludge and scum and more particularly to flight attachment links in such chains on which sludge and scum collector flights are mounted.
2. Reference to Prior Art
Wastewater treatment plants and refineries include liquid wastewater treatment tanks that use sludge and scum collector apparatus to scrape settled sludge from the bottom of the tank and to skim floating scum from the surface of the liquid wastewater. These wastewater treatment tanks may be over 300 feet long and can have widths greater than 20 feet. The collector apparatus in such tanks normally includes a pair of laterally spaced apart parallel endless chain loops comprising block links pivotally interconnected by connecting links for articulation about pivot pins. The chains are trained to travel around chain sprockets carried by cross shafts at each end of the tank. Elongated collector flights to extend transversely across the tank and their opposite ends are connected to the chains. The links in the chain on which the collector flights are mounted are referred to as flight attachment links. One of the cross shafts of the collector apparatus is driven causing the pair of chain loops to simultaneously revolve thus moving the chains along a straight line of travel to carry the flights mounted on the flight attachment links along the bottom of the tank and then along the surface of the water to move sludge and floating scum into collection areas. A collector apparatus of this type is shown in U.S. Pat. No. 3,313,422 issued Apr. 11, 1967 to W. R. Swenson.
In such prior art arrangements each flight attachment link includes a flight attachment support. When initially installed the flight attachment links on each of the spaced parallel chain loops are precisely aligned transversely in opposed relation which automatically aligns their associated flight supports. The collector flights are then secured to the transversely aligned supports. As previously mentioned these tanks can be over 20 feet wide and the flights are of a length that they span the full width of the tank.
In operation, the flights may bow under the loading force imposed by the weight of the material being moved. This bowing of the flights can apply a torsional stress to the flight supports and their associated attachment links which may result in premature failure thereof. The chains can also misindex on the sprockets. When chain misindexing occurs the flight attachment links are no longer transversely aligned, but remain interconnected by the transverse collector flights which impose forces tending to twist the attachment links. This places stress on the flight attachment links and flight supports.
One common way of dealing with such torsional stress was to reinforce all portions of the flight attachment links and flight supports to make them as strong and rigid as possible. This requires that the flight attachment link and paddle plate be of a reinforced heavy duty rigid construction which increases the cost of the chain manufacture, its weight and the power required to drive the chain. It has also been suggested in U.S. Pat. No. 5,165,522 issued Nov. 24, 1992 to Uttke et al. to design the flight attachment link and flight support to have significant torsional flexibility. A flexible link and flight support provides excellent service but requires a complex flight attachment link design and configuration which increases the cost of manufacture.